Various diffusers have been utilized in filters, such as a sand filter, for distributing unfiltered fluid to filtering media positioned therebelow. For instance, U.S. Pat. No. 3,493,116 discloses a swimming pool filter equipped with an overdrain which includes a disk-like head immovably mounted on the top end of an upright pipe by a conical fitting.
Double-tiered diffusers have also been used in connection with filters in the past. More particularly, such a diffuser typically includes an upper tier, which has an outer tubular extension projecting downwardly therefrom. The filter diffuser is also provided with a lower tier having a trough, which is mounted at an upper end thereof for supporting the upper tier thereon, and an inner tubular extension, which projects upwardly from the trough. The inner tubular extension of the lower tier is snap-fitted into the outer tubular extension of the upper tier, whose inner diameter is substantially equal to the outer diameter of the inner tubular extension, such that a tight fit is formed between the outer and inner tubular extensions, thereby inhibiting the upper tier from moving laterally relative to the lower tier. In such circumstances, when a closure dome is applied to an access opening during the assembly of the diffuser in an associated filter housing so as to seal the access opening and so as to secure the diffuser, the diffuser cannot adjust itself in response to the dome's application if the upper tier is not properly centered in relation to the access opening. This generally results in the diffuser being installed in an improper orientation and thereby causes stress on various pipe joints associated with the diffuser.